1. Field
The embodiments described below relate generally to the delivery of therapeutic radiation to a patient. More specifically, some embodiments are directed to treatment verification systems used in conjunction with such delivery.
2. Description
According to conventional radiation treatment, a radiation beam is directed toward a tumor located within a patient. The radiation beam delivers a predetermined dose of therapeutic radiation to the tumor according to a pre-established treatment plan. The delivered radiation kills cells of the tumor by causing ionizations within the cells.
Radiation treatment plans are designed to maximize radiation delivered to a target while minimizing radiation delivered to healthy tissue. These goals might not be achieved if the radiation is not delivered exactly as required by the treatment plan. More specifically, errors in radiation delivery can result in low irradiation of tumors and high irradiation of sensitive healthy tissue. The potential for mis-irradiation increases with increased delivery errors.
Delivery errors may arise from many sources. For example, a patient position may vary from that required by a treatment plan, internal patient anatomy may be displaced with respect to external visible markers, and/or characteristics (e.g., flatness, symmetry and penumbra) of the delivered radiation beam may not match beam characteristics on which the treatment plan is based. Devices used to shape the radiation beam may provide another potential source of errors.
Generally, incorrect positioning of beam-shaping devices may result in a radiation field that is not shaped as required by a treatment plan. For example, a treatment plan may specify a degree of rotation for a multi-leaf collimator used to shape a radiation beam, and may also specify particular positions for each jaw and leaf contained therein. Any deviance between the actual rotation/positions and the specified rotation/position may result in delivery errors. Unexpected radiation leakage around or between the jaws/leaves may also result in errors.
Quality assurance procedures are typically performed periodically and/or prior to radiation treatment in order to detect and correct potential radiation delivery errors. These procedures are particularly time-consuming and often inefficient. Delivery errors may also be identified after treatment, in which case a next fraction may be modified in an attempt to account for the errors. The latter approach is particularly troublesome, as accidental delivery of radiation to sensitive tissues obviously cannot be undone.
In view of the foregoing, what is needed is a system to efficiently identify potential delivery errors. It is further desirable to identify such errors during radiation treatment so that treatment may be suspended and/or modified.